The invention belongs to the methods of hot hydrostatic pressing, wherein the blanks are heated to temperatures above the 600-700° C. range, such as hot extrusion of metals and sintered billets, HIP-ping (Hot Isostatic Pressure), hot compacting of powders and deposited powder materials, plastic deformation under high isostatic pressure, etc.
In the practice, hot blanks heated up to the above temperature range are pressed using such working liquids as special silicon oils and heat-resisting grease. At a higher temperature range, in the so-called “forging interval” about 1000-2000° C., it is known to press blanks and materials in a media of gases or colloid graphite.
Pressing in inert or reactive gases is performed in pressurized autoclaves (gasostats) at pressures up to 1500-2000 atm and temperatures up to 2000° C. A basic shortcoming of the “gas” pressing is the relatively low attainable pressure and the high complexity of the equipment. The power consumption per unit weight of the blank is high due to the great compressibility of the working gas and the impossibility to recuperate the compressed gas energy. Since the blanks are heated inside the gasostat, the working gas and the autoclave chamber are heated as well, contributing to energy losses.
The low attainable pressure in the “gas” pressing is a major limitation for such pressing methods as HIP-ping and compacting processes, where it significantly prolongs the seasoning time of the blank. A typical gasostat working cycle in such a process takes 6-8 hours. Besides, the low pressure prevents obtaining of high-quality compacted powders and deposited materials.
The pressing of hot blanks in “pseudofluid” media such as colloid graphite may be carried out at very high pressures and is energy-efficient since the “pseudofluid” has low compressibility. However, this media is characterized by a considerable internal friction, which makes the pressure non-uniform over the working volume. Colloid graphite is also prone to undesirable chemical reactions with the blank material.
JP 01269509 discloses a method of using a low-temperature working liquid for pressing resin powder at high temperature by filling the heated powder in a heat-insulated capsule with heat-insulated rubber cover and pressing the capsule in a hydrostatic press by means of said working liquid. Here the capsule and the cover protect the working liquid from contact with the heated powder during the whole processing time. Consequently, the method is limited to temperatures that a rubber cover may endure, e.g. 500-600° C.